FIG. 1 shows a prior art electromagnetic alarm switch assembly 1. The assembly generally includes a magnetic switch 2 and a magnet 3 that are separate components and are mounted in close proximity to each other on a closed door 4 and door frame 5 (or window and window frame). In operation, as the door 4 is opened and the switch 2 and magnet 3 move apart, at a predetermined distance the effect of the magnetic field of the magnet is no longer imposed on the switch, the switch reacts, and the alarm sounds. Typically, the switch 2 is normally "open," meaning that the alarm is on. However, when the door 4 is closed and the magnet 3 is in close proximity, the magnet 3 holds the switch 2 in a closed (alarm off) position. As the door 4 is opened and the magnet 3 moves away from the switch 2, the switch 2 reverts to the normally open position, thus sounding the alarm. These types of switches can be easily circumvented simply by holding a magnet in close proximity to the switch 2 while the door is opened, thereby maintaining the switch 2 in the closed position.
FIG. 2 shows another prior art electro-magnetic alarm switch assembly 6. The assembly 6 includes a housing 7 having a first 8 and second 9 portion. The first portion 8 includes a switch and the second portion 9 includes a magnet. The assembly 6 is designed to function with a slidable door latch 10, such as is often used on a raisable overhead door. The closed door latch 10 lies at rest through the open mid-portion 11 of the "U". The switch is normally "closed" (alarm off). When the slidable latch 10 is in the closed door position, as shown, interaction between the magnet and the switch is blocked by the latch 10 (as shown by arrows A). When the slidable latch is withdrawn, as to open the door, the magnet causes the switch to open, thereby sounding the alarm. A drawback to this design is that the assembly 6 can easily be "tampered with" by inserting into open mid-portion 11 a metal "dummy" latch before withdrawing the latch 10, thereby maintaining the block between the magnet and the switch and allowing the door to be opened while preventing activation of the alarm.
Other prior art alarm switches are known, however many of these are not provided for use with a slidable door latch. Examples of prior art alarm switches can be found in U.S. Pat. Nos. 5,673,021 to Woods and 5,668,533 to Jackson et al.
A long felt need exists for an alarm switch assembly that is provided for use with a slidable door latch and is substantially tamper-resistant.